Effectiveness drops to 28% to 31% when booster doses are given two to three months after the previous vaccination.
The updated ones Pfizer/BioNTech and Moderna’s booster mRNA bivalent vaccines against Covid-19 provide increased additional protection against new subtypes of the coronavirus in people who have had two to four doses of the older vaccines.
That’s according to a new study by scientists at the US Centers for Disease Control and Prevention (CDC), the first to evaluate the effectiveness of revamped vaccine formulations based on real-world, not laboratory, evidence.
The findings, published in the CDC’s Morbidity and Mortality Weekly Report, confirm initial results from the vaccine companies’ own laboratory studies, which showed that the updated bivalent vaccines after one month lead to the production of more antibodies against the BA.4/BA.5 subvariants of the Omicron variant, relative to the original monovalent vaccines.
The study, which involved more than 360,000 people, compared the boosted updated bivalent vaccines (targeting both the original coronavirus and Omicron’s newer BA.4 and BA.5 subvariants) with the same companies’ original vaccines. The study found that comparativelypeople 18-49 get the most benefit from updated vaccines years compared to older people.
More specifically, according to Reuters, when the updated bivalent Covid-19 vaccine is given eight or more months after the previous dose, its relative additional effectiveness – compared to that of the original in preventing symptomatic disease – is 56% among 18-49 year olds, 48% among 50-64 year olds and 43% among over 65 year olds. The improved efficacy drops to 28% to 31% when booster doses are given only two to three months after the previous vaccination.
So far in the US only 35 million people or about 10% of the population have updated bivalent vaccines. The researchers stressed that everyone should get the booster shots, but acknowledged that the shots may not be as effective in the future as the coronavirus continues to evolve. Indicatively, during the last two months, sub-variants BQ.1 and BQ.1.1 tend to dominate in the US, surpassing BA.5.
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